Copper refining



mama Feb. 21, 1928.

UNITED STATES PATENT OFFICE.

ANTHONY G. DE GOLYEB, OI BROOKLYN, NEW YORK.

corrnn nnrmma.

Io Drawing.

oxygen.

In response to industrial and technical demands, many attempts have beenmade to produce oxygen free copper by direct refining methods andotherwise. While it has been possible heretofore-to produce oxygen freecopper by means of previously proposed methods,.copper so produced didnot have the necessary additional qualities of high metallic coppercontent, high electrical con-, ductivity, and freedom from dissolved oroccluded gas which, latter, resulted in gas or blow? holes in the solidcopper. Consequently, copper produced by previously proposed methodsdoes not possess the necessary properties and qualities to meet thegeneral industrial and technical requirements, hence, none of suchpreviously pro-- posed processes have been of commercial importance.

I have discovered that by means of the hereinafter described process Ican produce copper which is entirely free from dlssolved or occludedgas, such as carbon monoxide, and entirely freefrom oxygen. Furthermore,the copper so produced contains lower percentages of various impurities,such as iron and sulphur, than copper produced by heretofore knownpyrometallurgical methods, and copper produced by means of the presentinvention is entirely free from residual impurities resulting fromreagents usedin eifecting complete removal of oxygem By reason of thecombined advanta eous factors-absence of dissolved or occ uded gases,absence of oxygen,-and high metallic copper contentcopper produced bythe operation of the present invention possesses higher percentage ofelectrical conductivity, higher tensile strength and greater reductionin area and'per'centage of elongation than chipper refined bypreviouslyknown metho s.

The present process is equally adapted for the refining of cathodecopper produced by electrolytic refining and the direct refining ofcopper bearing material which has not been refined electrolytically,such as blister Application filed A ril 16, 1927. Serial ll'o. 104,443.

copper, cement copper,scra copper, etc. It is also adapted for use in0th the production of cast sha es to be used in the production of wire,tu sheets and other wrought articles, and for the production of finishedor semi-finished castings in sand or other molds, particularly castingshaving high electrica conductivity, high tensile strength and excellentmachining qualities.

Before describing my invention I give, for the purpose of com arison, anoutline of the pyrometallurgica method which has heretofore beengenerall used for the refining of co per, and the a ditional operationsrequire for the production of deoxidized cop er.

Electro ytic copper in the form of cathodes has an average metallic copr content of 99.97 5%, and an electrical con uctivity of 101% or more(Matthissen standard), and is substantially free from oxygen. However,cathode oopper is not in suitable condition for rolling or otherworking, and must be subjected to a pyrometallurgical refiningprocess'before itcan be rolled, drawn, etc

.from. the fuel flames.

When the charge ismolten, air is blown into the copper until the bathconsists of the saturated copper-copper oxide eutectic, containing 39%oxygen, and, in addition, some free cuprous oxide, so that the bathgenerally contains from 45% to .55% o gen. Oxidation in thismannerremoves su stantially all sulphur from the bath, as sulphur dioxide; andsubstantially iron, and a portion of certain other impurities, such asarsenic and antimony. The latter impurities are removed from the co r asoxides which enter the slag. Fo owing oxidation, a large proportion ofthe slag is removed.

' the requisite reduction in area and elonga-v Partial deoxidation ofthe bath is then undertaken by poling i. e., logsor poles of green woodare introduced under the surface of the metal, the wood. being convertedinto charcoal which in turn reacts with the euprous oxide of the bath.Reduction of the cuprous oxide in this manner is continued until theoxygen content of the bath is between .035% and 055%, Within which rangethe metal is said to be tough pitch copper. At this stage the copper iscast into wire bars, cakes, ingots, etc. a

The poling operation requiresfrom 3 to 4 hours, and from 4 to 6 hoursare consumed in casting, and during these periods the copper againabsorbs appreciable amounts of sulphur, as well as iron and otherimpurities.

In the refining of copper by the above described method it is essentialthat the oxygen content be maintained within the range of from 035% to055%, as when the oxygen exceeds approximately .060% the cast copper isunsound, apparently due to the presence of a gas. Furthermore, therelatively high oxygen content reduces the percentage of reduction inarea and elongation to such an extent that the copper does not possess'suflic-ient ductility for mechanical working.

In a similar manner, when the oxygen content is reduced to less than035% the cast copper is unsound, the metal invariably rising or swellingin the molds, due to the presence of carbon monoxide, and possibly othergas, and such copper, termed over-poled, is' also unsuitable formechanical working by reason of porosity, impaired ductility, lowelectrical conductivity, etc.

It will be apparent, therefore, that the poling operation can not beutilized for the production of oxygen free copper having tion, i. e.,ductility, tensile strength, electrical conductivity and other essentialor desirable physical properties.

Copper produced by the above described pyrometallurgical method,generally termed electrolytic copper, thus contains between 035% and.060% oxygen and has a metallic copper content of between 99.900% and99.960%. Wire of approximately .080 of an inch diameter drawn from suchcopper and annealed, will have an electrical conductivity of from 99.5%to 100.8%; a'reduction in area of from 35% to 47%; elongation in 10 inchlengths of from 30% to 38%, and will show an average of between 38 and44 twists in 6 inch lengths.

Therefore, the metallic copper content and the percentage of electricalconductivity of copper-refined by such methods are substantiallv lowerthan the copper content and electrical conductivity of the originalcathode copper. Furthermore, the presence of oxygen, in the form ofcuprous oxide, in such copper renders it entirely or partiallyunsuitable for many industrial applications.

Many attempts have been made to pro duce oxygen free copper by means ofa combination of the above described method and the additional operationof adding a metallic deoxidizing agent, such as phosphorus or silicon,to the poled copper, i. e., the copper containing between .035% and 060%oxygen.

While it is possible to produce copper which is substantially oxygenfree by such methods, the cast copper is invariably unsound, due tothe-presence of gas in the molten metal, hence it is not suitable forrolling, drawing, or other mechanical working. Furthermore, such copperalways contains impurities in the form of residual metallics of thedeoxidizing agent, hence the 85 percentage of electrical conductivity ismaterially reduced, being. in such cases, between 85% and 92%(Matthissen standard), so that the copper is not suitable for use inwire or other wrought forms forthe transmission vof electrical energy.

It will be apparent that it is not possible to produce copper, bymethods heretofore available, which possesses the following combinedproperties: (a) entire freedom from oxygen; (6) entire freedom fromdissolved or carbon monoxide or other gases; (0) metallic copper contentof 99.970% or higher; (d) electrical conductivity of 100.5% (Matthissenstandard) or higher.

By means of the process of the present in vention I convert cathodecopper into any desired shapes or forms for use in the manufacture ofwrought products, or for use as finished or semi-finished castings, andthe copper so produced is characterized by entire freedom from dissolvedor occluded carbon monoxide and other gases; entire freedom from oxygen;a metallic. copper content as high as, or higher than in the orig inalcathode copper; a percentage of electrical conductivity as high orhigher than that of the original cathode copper; high tensile strength;high percentage of reduction in area, "e. g., approximately"80% in 116the case of annealed wrought products. Furthermore, by means of thisinvention I also refine copper containing material which has not beenrefined electrolytically, such as blister copper, cement copper andscrap 1 copper, and convert such copper into any desired forms for usein the manufacture of wrought products, or for use in finished orsemi-finished castings, and the copper so produced is characterized by;entire free dom from dissolved or occluded carbon monoxide and othergases; entire freedom from oxygen; a metallic copper content appreciablyhigher than in the original copper trical conductivity higher than thatof the original copper containing material; a relatively high percentageof reduction in area e. g., or more in the case of'anneale wroughtproducts.

The process of the present inventlo is based upon my discovery that,under certain conditions, carbon monoxide is soluble in molten copper. Ihave found through extensive research that carbon monoxide which isgenerated or formed within molten copper dissolves or is occluded in thecopper.

I have further discovered that when the percentage of oxygen exceeds adefinite amount, approximately 10% of the total Weight of the bath, thatany carbon monoxide formed within the copper is more or lesssimultaneously converted into carbon dioxide, which is not soluble inmolten copper. On the contrary, when the percentage of oxygen in thebath is less than approximately 10%, an appreciable proportion of carbonmonoxide generated or formed within the molten copper remains dissolvedor occluded therein as long as the copper is molten.

It appears, therefore, that 10% is what may be' termed a critical oxygenoint, i. e., when the oxy en content excee s this amount there isevidently a mass reaction of cuprous oxide with carbon monoxide,-

probably according to the following:

C11 0 CO 2Cu CO and, as carbon dioxide is not soluble in 1110]- tencopper such gas readily escapes from the bath; on the other hand, whenthe oxygen content is less than this amount the mass reaction .ofcuprous oxide and carbon monoxide does not'take lace, with the resultthat a portion or all of the carbon monoxide present within moltencopper remains occluded or dissolved therein.

When molten copper containing carbon monoxide in solution, or otherwise,is cast the carbon monoxide is not released until the copper has cooledto a temperature which is relatively not much higher than the freezmgpoint of copper, the result being that carbon monoxide is expelledshortly prior to the formation of the crystal and thus tends to becomemore or less concentrated along the crystal boundaries with theconsequent formation of gas holes. Such gas holes are, of course,readily detected in the case of oxygen free copper. However, in the caseofcast copper containing from 035% to 055% oxygen the occurrence ofholes due to the presence of'carbon monoxide in the copper when moltenis not as readily apparent, unless the amount of carbon mon- It appearsthat oxide has been excessive. in such oxygen containing cop r thecopper-copper oxide eutectic, WhlC occurs on the crystal boundaries,acts to retain a relatively large amount of carbon monoxide, and in thiscase the holes caused by the (gas are smaller and less apparent due toisseminat'ion of the gas.

.of the process of this invention the presence of additional gas orgases in molten copper may be disregarded as they are apparentlyentirely eliminated by the methods used to prevent the occurrence ofcarbon monoxide in molten copper.

The process of the present invention comprises the following essentialoperations ((1) Partial reduction of the cuprous oxide in the moltencopper by reaction with carbon.

(1)). Stopping the reduction with carbon before the oxygen content hasbeen reduced to the critical oxygen point, i. e., the point at and belowwhich there is not suflicient oxygen or cuprous oxide in the bath toreact with all carbon monoxide present in the copper to convert it tocarbon dioxide; this critical point being approximately .01% oxygen.

(0) Subsequent removal of all remaining oxygen by means of subjectingthe oxygen and oxygen compounds of the bat-h to reaction with ametallic'reducing agent, the reaction of which with oxygen or oxygencompounds does not generate carbon monoxide in appreciable amounts.

The process ofmy invention may be successfully carried into effect inthe following manner:

Copper or copper bearing material ma be melted in any furnace to which asufli cient volume of energy in the form of heat may be supplied to meltthe copper, and maintain it in a thoroughly molten condition during thenecessary operations. When the copper is not sufiiciently oxidizedcoincidental with melting, and when the bath absorbs an appreciableamount of sulphur or otherimpurities during melting oxidation by blowingis necessary.

After the desired amount of oxidation has been effected, the bath ispartially deoxidized by the introduction of carbon into the v metal.This may be accomplished by poling in the usual manner, the introductionof charcoal, coke, or other carbonaceous materials into the copper, suchas by means of immersion, agitation or otherwise. During the artialdeoxidation operation samples of t e copper may be taken from time totime to determine the progress of reduction of ox gen, or this operationmay be timed,

that 1s, an approximate weight of carbon may be allowed to react withthe oxygen of the bath for a predetermined length of time.

- Immediately following the partial deoxidation operation, one or moremetallic reducing agents are introduced into the molten metal, andallowed to react with the remaining oxygen. I have found thatsilicon,manganese, phosphorus and a number of boron containing reagentsmay be successfully used as the metallic reagents in removing all of theoxygen from the bath. The purpose for which the copper is intended willusually determine the proper reagent to employ. For example, when it isdesired to produce as free and oxygen free copper having an e ectricalconductivity of more than 100% it is essential to use a metallicreducing agent which will not alloy or otherwise combine with the copperto lower the electrical conductivity. In a similar manner when it isdesired to produce copper billets possessing the maximum ductility forthe manufacture of seamless tubes by the piercing method it is also ofadvantage to use a metallic reducing agent which will not combine withthe copper nor result in residual impurities therein, either or both ofwhich conditions would tend to make the piercing operation moredifficult.

When all of the oxygen has been removed the copper is ready for castinginto any desired commercial shape, or into sand or other molds for theproduction of finished or semi-finished castings.

While the process of the present invention can be successfully andsatisfactorily carried into effect according to the above generaloutline of operations, for the purpose of further illustration I giveherewith a preferred method of operation.

In this particular scheme of operation, I use a combination stack andreverberatory furnace for melting the copper, and use oil or powderedcoal as the fuel for heating the furnace. The solid copper, which may becathodes or metal which has not been refined electrolytically, ischarged into the '50. stack, and as it passes down through the stack itis preheated and finally melted. The molten metal flows out of the stackinto the hearth of the reverberatory portion of the furnace. It will beapparent that the character of the combustion gases in the stack portionof the furnace may be closely regulated and controlled, thus givingadvantageous melting conditions. Furthermore, by melting in this mannerthe molten metal does not remain in contact with the fuel flames formore than a few minutes, consemolten condition in the second furnace andpartial removal of oxygen is accomplished by reaction of carbon with theoxygen and oxygen compounds of the bath. Such removal of ox gen is,according to my process, stopped be ore the cuprous oxide content isreduced to the critical oxygen percentage. The bath is then partially orentirely covered with charcoal or other carbonaceous material for thepurpose of maintaining a neutral or reducing atmosphere within thefurnace; or the bath may be covered with oxygen compounds, such as lime,magnesia, etc., which are inert under the prevailing conditions. Afterthe copper has thus been protected from possibility of oxidation by theatmosphere of the furnace, a metallic reducing agent is introduced intothe copper for the purpose of removing all remaining oxygen. Themetallic reducing agent employed must be capable of reacting with oxygenand oxygen compounds of copper under the physical conditions prevailingwithin the furnace, and it is essential that such reactions do notgenerate appreciable amounts of carbon monoxide. hen it is desired toproduce copper having an electrical conductivity of 101% or higher(Matthissen standard) it is necessary to use a metallic reducin agentwhich does not dissolve in or ot erwise combine with, or contaminatecop,- per. As an example of reducing agents which are suitable for thispurpose I cite aluminum boride, calcium boride and silicon boride. Whenelectrical conductivity is not an objective other metallic reducingagents, such, for example, as phosphorus, silicon or manganese may beused.

When the oxygen has been entirely removed the copper is cast into anysuitable I molds in the usual manner.

Copper produced by means of the process of this invention ischaracterized by entire freedom from dissolved or occluded carbonmonoxide and entire freedom from oxygen and oxides, consequently,castings made therefrom are characterized by entire freedom from holesand other defects due to the presence of gas or oxygen in the moltenmetal.

A further distinctive advantage of the present invention is that the gasfree and 0 n free co per produced by means of tli i s process ibssesseshigher percenta e of electrical conductivity, greater t e strength andgreater percentages of reduction in area and elongation than oxy enfree, or oxygen containing copper which as been refined by previouslyknown methods.

. It will be apparent that in the case of copper which has been oxidizedto an ap reciable extent that the major ortion 0 reduction of the oxygenof the ath is accomplished by means of carbon, which is of decidedeconomical advantage.

The terms critical oxygen point and critical oxygen percentage usedherein and in the appended claims refer specificallyto the percentage ofoxygen present in molten copper in the form of cuprous oxide, and suchterms are used to designate the percentage p oint at which cuprous oxideceases to react with carbon monoxide to oxidize the latter com ound.

I have ound also that copper which has been refined by means of theprocess of the present invention and which contains relatively smallpercentages of oxygen and/or dissolved or occluded carbon monoxide willpossess physical properties approximatin the physical properties ofsimilarly refine copper which is entirely free from carbon monoxide andoxygen. Although the presence of even such relatively small amounts ofoxygen, chiefly in the form of cuprous oxide, will render copperunsuitable or undesirable for various applications, I have found thatcopper refined by means of this process and which is substantially freefrom included carbon monoxide and oxygen can be used for certainindustrial applications.

Therefore, the herein described refining process may be advantageouslyutilized for the production of copper which is substantially free fromdissolved or occluded carbon monoxide and/or oxygen. It will be evidentthat such small amounts of'these impurities may be allowed to remainintentionally or otherwise in the refined copper without departing fromthe scopeof my present invention. As an example, in the operation of theprocess a small percentage of oxy may be allowed to remain in the coppery the use of a quantity of metallic reducing agent which is insuflicientto remove all of the oxygen in the molten metal. It will be understood,however, that the physicalprop erties of such cop r containingimpurities in the form of car on monoxide, other oxygen compounds or oxyn will not be entirely the same as the copper which is entire y freefrom such 1mpurities.

By the term substant ally free from oxygen used herein and in theappended claims, I refer specifically to copper contaming not more than.008% oxygen.

than the critical percentage at, and

ysical properties of I claim:

1. The method of producing copper which is entirely free from dissolvedor occluded gas and entirely free from oxygen compounds which comprisesreducing the oxygen content of the copper, while molten, by reaction ofcarbon with the oxygen of the bath to a point 'above the critical oxygenpercentage at, and below which carbon monoxide is retained in moltencopper; subsequently re moving from said molten copper all remalningoxygen by subjecting such oxygen to reaction with a metallic reducingagent, the reaction of which does not generate carbon monoxide.

- 2. The method of producing copper which is entirely free from includedgas and entirely free from oxygen compounds which comprises reducing theoxygen content of the copper, while molten, by reaction of carbon withthe oxygen of the bath to a point above the critical oxygen percentageat, and below which mass reaction of cuprous oxide with carbon monoxidedoes not occur; subsequently removing from said molten copper allremaining oxygen by subjecting such oxygen to reaction with a metallicreducing agent, the reaction of which does not generate carbon monoxide.

3. The process of producing copper which is entirely free from carbonmonoxide and entirely free from oxygen in any form which comprisesreducing the amount of cuprous oxide in molten. copper by reaction withcarbon to a point above the critical percentage at, and below whichreaction of cuprous oxide with carbon monoxide 'does not proceed at thetem erature revailing in the bath; subsequenty removlng all remainingoxygen by subjecting such oxygen to reaction with a metalllc reducingagent, the reaction of which does not generate carbon monoxide.

4. The process of producing copper which is entirely free from cuprousoxide and carbon monoxide which comprises reducing the amount of cuprousoxide in molten cop r by reaction with carbon to a point hig er belowwhich mass reaction of cuprous oxide with carbon monoxide does notoccur; subsequently) removing all remaining cuprous y subjecting suchcuprous oxide tooxide reaction with a metallic reducing agent, thereaction of which does not generate carbon monoxide. V l

.5. The process of producing cast copper which is entirelfvmfree fromoxygen and substantially free 111 gas holes and other defects due to thepresence of cuprous oxide and dissolved or occluded gas which comprisesreducing the amount of cuprous oxide in molten copper by reaction withcarbon and carbon monoxide to a point higher than the criticalpercentage at, and below which reaction of cuprous oxide with carbonmonoxide does not proceed in such a manner as to remove substantiallyall carbonmonoxide from the metal; subse uently removing all remainingoxygen y subjecting such oxygen to reaction with a metallic reducingagent, the reaction of which does not generate carbon monoxide.

6. The process of producing cast copper which is entirely free fromoxygen, substantially free from gas holes and other defects caused bycarbon monoxide, and which has a minimum electrical conductivity of 101%(Matthissen standard) which comprises reducing the amount of oxygen inmolten copper by reaction with carbon and carbon monoxide to a pointhigher than the critical percentage at, and below which carbon monoxideis retained in the molten copper; subsequently treating said moltencopper which contains oxygen, but is substantially free from carbonmonoxide, to remove all remaining oxygen by subjecting such oxygen toreaction with a metallic reducing agent which is not soluble in moltencopper and the reaction of which does not generate carbon monoxide.

7. The process of producing cast copper which is entirely free fromoxygen and substantially free from holes and other defects caused bycarbon monoxide, and which is further characterized by a minimummetallic copper content of 99.985%, a minimum electrical conductivity of101% (Matthissen standard) anda minimum reduction of area, in theannealed condition, of 74%, which comprises reducing the amount ofoxygen in molten copper by reaction with carbon to a point higher thanthe critical percentage at, and below which carbon monoxide is retainedin molten copper; subsequently removing all remaining oxygen bysubjecting such oxygen to reaction with a metallic reducing agent whichis not soluble in molten copper, and the reaction of which does notgenerate carbon monoxide.

8. As a step in the process of producing copper which is entirely freeof carbon monoxide and oxygen in any form by means of reducing a portionof the oxygen contained in molten copper by reaction with carbon,stopping the reduction of cuprous oxide with carbon while suflicientcuprous oxide remains in the bath to react with all carbon monoxidepresent in such a manner as to oxidize such carbon monoxide to carbondioxide or other compounds which are not retained in molten copper.

9. The process of producing copper which is entirely free from dissolvedor occluded carbon monoxide and from oxygen which comprises meltingcopper directly in heat enerated by combustion of carbonaceous fuel,allowing the molten copper to flow consubstantially prises removingoxygen from molten coptinuously from the melting zone of the furnace toa hearth situated at a lower elevation than said melting zone;intermittently removing molten copper from said hearth, and transferringit to a second furnace in which the copper is maintained in a moltencondition by the direct heat of the combustion of carbonaceous fuel;reducing the oxygen content of the molten copper in said second furnaceby reaction with carbon to a point higher than the critical oxygenpercentage at, and below which molten copper retains carbon monoxide;subsequently removing from said molten copper all remaining oxygen bysubjecting the oxygen and oxygen compounds to reaction with a metallicreducing agent, the reaction of which does not generate carbon monoxide.

- 10. The process of producing copper which is entirely free fromcuprous oxide and from dissolved or occluded carbon monoxide, and whichis further characterized by a minimum metallic copper content of 99.985%and a minimum electrical conductivity of 101% (Matthissen standard)which comprises melting copper directly in the products of combustionofcarbonaceous fuel, intermittently removing molten copper from themelting furnace and transferring it to a second furnace where saidcopper is maintained in a molten condition by direct exposure to theproducts of combustion of carbonaceous fuel; reducing the cuprous oxidecontent of said copper in said second furnace to an amount which is inexcess of the percentage of cuprous oxide necessary to react with allcarbon monoxide present and oxidize it to carbon dioxide or othercompounds which are not soluble in molten copper; subsequently removingfrom said molten copper all remaining cuprous oxide by subjecting suchcuprous oxide to reaction with a metallic reducing agent which is notsoluble in, and does not alloy or otherwise combine with molten copper,and the reaction of which does not generate carbon monoxide.

11. In the fprocess of producing copper ree from oxygen, which comper byreaction with carbon; the step of removlng carbon monoxide whichconsists in stopping the removal of oxygen with carbon while sufiicientoxygen remains in the bath to react with substantially all the carbonmonoxide present and permitting said oxygen and carbon monoxide to reactto form carbon dioxide or other compounds which are not retainable bymolten copper.

12. The process of producing copper substantially free from oxygen gasholes and other defects caused by the resence of dissolved or occludedgas whic comprises reducing the amount of oxygen in molten copper byreaction with carbon to a point sufiiby subjecting such oxygen toreaction with ciently higher than the critical percentage a metallicreducing agent, the reaction of at and below which reaction of cuprouswhich does not generate carbon monoxide. 10 oxide with carbon monoxidedoes not pro- Signed at New York in the county of 5 ceed to removesubstantiall all carbon mon- New York and State of New York this oxidefrom the metal; an subsequently retwenty-fourth day of March, A. D.1927. moving substantially all remaining oxygen ANTHONY G. DE GOLYER.

